2013 Peterbilt 386, 72" sleeper Shaking cab

They should be lined up/in phase between the transmission and front axle. The ones between the axles should also be in phase. But the shaft between the axles and the one in front will not and do not have to be in phase.

 

You state the shaking only happen with an empty dump trailer, what happens with the trailer unhooked and going down the highway?

 

Just because the tires are "like new", they could have hit something. Driveshaft balance? Axle bearings? Bent rim? I doubt it's coming from the front, and you are running out of things it could be. I'd say the tires.

 

OK

When you have issues with shaking or abnormal tire wear, DO NOT EVER BUY USED TIRES ... NEVER EVER

If there is abnormal wear, replace all the shocks and get the truck in for an all-wheel alignment. Have them check the bushings and driveline while they have the truck on the rack. You should do the shocks and alignment every year to 18 months.

That said, change the shock(s), airbag and leveling valve for the cab, maybe even the mounts, it seems that may be the problem.

 

Drive tire out of round will cause the shake and steering wheel remain smooth.